Cyclopentobarbital sodium (Cyclopal, Dormisan) is a barbiturate derivative invented in the 1940s.[1] It has sedative and anticonvulsant properties, and was used primarily as an anaesthetic in veterinary medicine.[2] Cyclopal is considered similar in effects to phenobarbital but lasts almost three times as long, and is considered a long-acting barbiturate with a fairly slow onset of action.